Sterilization is the destruction of any virus, bacteria, fungus or other micro-organism, whether in a vegetative or in a dormant spore state.
Conventional sterile processing procedures for medical instruments involve high temperature (such as steam and dry heat units) or chemicals (such as ethylene oxide gas, hydrogen peroxide or ozone).
Some complex medical devices, such as flexible endoscopes, do not accept high temperature and can therefore not be sterilized with a high temperature technique.
Sterilization methods and apparatus using gaseous chemical sterilants are well known. Sterilizers using hydrogen peroxide as the chemical sterilant are widely used. The hydrogen peroxide is generally supplied as an aqueous hydrogen peroxide solution. This solution is normally evaporated prior to injection into a sterilization chamber of the sterilizer. Evaporation is achieved by heating of the hydrogen peroxide solution, by subjecting the solution in the sterilization chamber or in a separate evaporator to a sufficient vacuum to evaporate the solution, for example by applying a vacuum to the sterilization chamber, or any combination thereof. After evaporation of the hydrogen peroxide solution, the atmosphere in the sterilization chamber includes water vapor and hydrogen peroxide gas. It is a disadvantage of such processes that the water vapor tends to condense on articles upon evaporation of the hydrogen peroxide solution into the chamber, with the resulting layer of condensed water on the articles to be sterilized interfering with the sterilizing action of the hydrogen peroxide gas. Numerous apparatus and process modifications have been developed to address this problem, all of which are aimed at limiting the relative humidity in the sterilization atmosphere during evaporation of the hydrogen peroxide solution and/or during the sterilization process. However, these modifications invariably increase operating cost, sterilization complexity and/or sterilization cycle times. Moreover, hydrogen peroxide solution based processes may still be unsatisfactory regarding the sterilization of specific complex articles with long lumens.
Many hydrogen peroxide sterilizers include a plasma generator in the sterilization chamber to minimize residual hydrogen peroxide that could remain on the sterilized articles, while helping to improve the sterilization process. Although such a technique seems to efficiently minimize residual hydrogen peroxide, it further increases the complexity and manufacturing cost of the sterilizers.
Sterilization processes using both a hydrogen peroxide solution and ozone gas have been developed for the sterilization of complex articles with long lumens. International patent application WO2011/038487, which is incorporated herein by reference, discloses a method for sterilizing an article by sequentially exposing the article to hydrogen peroxide and ozone. Although ozone based processes are satisfactory with respect to the sterilization of complex articles with long lumens, such as flexible endoscopes, material compatibility may still remain a challenge for specific medical devices.
Sterilization processes based on evaporating a hydrogen peroxide solution are generally sensitive to ambient conditions such as ambient temperature and relative humidity and therefore require to be operated in a specific limited range. The articles to be sterilized also have to be in predefined conditions before being sterilized. In some cases, the sterilizer is provided with a separate conditioning chamber particularly devised to adequately condition the load, i.e. conditioning the whole load to a specific temperature and relative humidity, before it is placed in the sterilization chamber. The added conditioning steps and chamber increase sterilization cycle times as well as sterilization cost and may not be very convenient for the operators. Moreover, the requirement for an additional chamber does not allow for a compact design of the sterilizer.
Various conventional hydrogen peroxide sterilizers use sterilant capsules of fixed volume, whereby the content of each capsule is evaporated and injected in a single step. However, due to the differences in vapor pressure and boiling point between water and hydrogen peroxide, this approach leads to disadvantageous effects when the sterilant used is an aqueous hydrogen peroxide solution. Upon sufficient heating, a hydrogen peroxide solution evaporates into water vapor and hydrogen peroxide gas. However, as the temperature of the solution increases, water tends to evaporate first due to its lower boiling point. Thus, upon evaporation of a large amount of water into a sterilization chamber, the initial supply of gas is generally water vapor. This water vapor may condensate on a load in the chamber due to temperature differences between the chamber atmosphere and the load. The resulting layer of condensed water is disadvantageous, since it blocks the hydrogen peroxide gas from reaching the load. Sterilization at the location covered by the water layer is only possible by dissolution of the hydrogen peroxide gas in the water layer, which requires longer cycle times and is disadvantageous, since the concentration of the resulting hydrogen peroxide solution at the covered location is always at most as high as the solution originally evaporated. To address this issue, processes have been developed to increase the concentration of the water vapor/hydrogen peroxide gas mixture during evaporation. However, although this approach increases the concentration of hydrogen peroxide within the layer of condensation on the load, the underlying problem of initially injecting exclusively water vapor during evaporation is not addressed.
More recently, in an attempt to provide more versatile sterilization procedures adapted to different types of loads, hydrogen peroxide sterilization apparatus and processes have been proposed, which include different cycle types for different types of loads. However, those cycles are adapted only to the type of load, and do not take into consideration load conditions such a temperature, humidity, volume and surface area of the load, since standard conditions of load temperature and humidity are assumed for each cycle type. Thus a selection of predefined sterilization cycles is provided to the operator, which are adapted to certain types of instruments to be sterilized. The operator of the sterilizer is then expected to correctly identify the type of load to be sterilized and select the cycle most appropriate for the load identified. Although this is a step towards more versatility in sterilization treatments, this approach requires the user to be sufficiently sophisticated to not only correctly identify the type of load, but also correctly select the most appropriate cycle from the predefined selection of cycles. This makes these sterilization processes and apparatus more difficult to use and requires the use of trained personnel.
It would therefore be desirable to provide a sterilization method and apparatus that would reduce at least one of the above mentioned drawbacks of known sterilization processes using gaseous or vaporized liquid sterilants.